Transmission of high-bandwidth information (e.g., greater than 20 THz) using wavelength-division multiplexing (WDM) systems is accomplished by dividing the wide-bandwidth into multiple lower-bandwidth WDM information channels (e.g., 50 GHz). The multiple lower-bandwidth WDM information channels are combined and then transmitted using the available bandwidth of the WDM system.
Traditionally, WDM modems (which include WDM information channel transmitters and WDM information channel receivers) operate completely independently from one information channel to another. This mode of operation was prompted by the reliance on oscillators (e.g., lasers) of poor quality (e.g., with poor phase stability, or a high degree of phase noise), making inherent phase and frequency tracking a complex task. WDM systems use carrier signals that include, but are not limited to: optical carrier signals, electrical carrier signals and radio-frequency (RF) carrier signals.
Each of the information channels of an optical WDM system relies on an optical emitter (e.g., a laser) that produces a carrier signal, onto which information is imprinted in a process called modulation (of the carrier signal) to produce modulated carrier signals. Transmission of a modulated carrier signal though an information channel over a transmission link of the WDM system unavoidably incurs impairments (e.g., chromatic dispersion, attenuation and other distortions) on the transmitted modulated carrier signal. Significant and sophisticated digital signal processing is performed at a WDM receiver to retrieve, or acquire, the information at the receiving end of the transmission link.
Independent laser emitters are typically used to generate the carrier signals in optical WDM systems. Being altogether independent devices, the properties of the underlying carrier signals for each information channel are not only distinct, but also vary independently and randomly over time. To successfully perform information retrieval, an independent WDM receiver is typically used for each information channel. In such systems, signal processing blocks of each WDM receiver are replicated and run independently. Even though each of the WDM receivers replicate the same signal processing chain, each of the WDM receivers may possibly arrive at different outcomes.
Thus, while there are numerous solutions for digital signal processing in coherent optical transmission systems, these solutions fail to meet the needs of the industry because the solutions replicate all or a portion of the same processing steps for each information channel (e.g., wavelength).
Some solutions attempt to merge processing of two or more information channels onto a single line card. However, processing for the two or more information channels is still performed independently, resulting in the same total complexity and power dissipation as the sum of processing for the independent information channels.